Health outcomes in the United States lag behind other developed nations despite health expenditures that are exceptionally high and growing. This disparity has led many to conclude that healthcare services are overused, a phenomenon driven by a perfect storm of patient, provider, and institutional determinants. Overuse has been defined as the provision of care in circumstances where the potential for harm exceeds the potential for benefit. While overuse is pervasive throughout the healthcare system, older Americans may be particularly at risk for receipt of services where the potential for harm exceeds the potential for benefit. This may include the use of screening tests when there are conditions causing substantial competing risks for death, therapies delivered at end-of-life that do not impact disease course or quality of life, therapies delivered without recognition of the heterogeneity among older patients due to frailty, polypharmacy in multimorbid patients, and care coordination failure when multiple specialists are involved in care. Overuse of healthcare puts patients at risks of adverse outcomes and has system-wide consequences, and yet this is poorly appreciated by patients, their families, and their clinicians. I seek this K24 award to support my effort as a researcher and mentor of talented young investigators as we work to understand overuse of healthcare and advance the practice of parsimonious medicine, a term reflecting the prudent delivery of care necessary for the patient's good. The overarching aim of this career development award is to work towards harm reduction for older patients through parsimonious healthcare use, and concurrently, advance my skills in patient centered outcomes research and train the next generation of researchers in this field. With my mentees, mentors, and colleagues, I will: a) systematically review the literature about determinants of overuse of healthcare resources; b) conduct a qualitative study via focus groups to understand how patients perceive overuse and its harms; c) use stated-preference methods to understand how older patients make decisions about their use of healthcare and how this varies in the presence of geriatric syndromes, and d) validate the Johns Hopkins Index of Overuse with additional data sources and explore the impact of Accountable Care Organization establishment on overuse of resources in older patients. The impact of this award is expected to be the completion of important research to inform the care of older adults, the advancement of a cohort of young investigators with skills to address these topics and others relevant to improved care delivery, and the personal advancement of my skills so that I can be an ever more effective researcher and mentor.